Polysiloxane-polyether block polymers containing polyethylene glycol ether groups that make them soluble in water are known from U.S. Pat. Nos. 2,834,748, 3,480,583, 3,600,418, and 3,629,310 and from British Pat. No. 802,467. Such block polymers do have foam-inhibiting characteristics, but these characteristics are not well developed in comparison with the characteristics of dimethylpolysiloxanes. Consequently, such polysiloxane-polyether block polymers have found no application as antifoaming agents but have been used, for example, to prepare polyurethane foams, where they act as foam stabilizers. (Cf. U.S. Pat. Nos. 3,398,104, 3,402,192, and 3,637,783 and British Pat. No. 1,293,331.)
Polysilane block polymers that contain polypropylene glycol ether groups and are insoluble in water are known from U.S. Pat. No. 4,028,218 and British Pat. No. 1,505,665. Mixed with highly dispersed silica or highly dispersed alumina, these block polymers have pronounced foam-inhibiting characteristics. They may contain additional components that enhance the foam inhibition, such as mineral oil or emulsifying agents that promote dispersion in aqueous systems. The presence of the above-mentioned highly dispersed oxides, especially silica or a resin containing silica, is required in all cases. However, this constituent makes the antifoaming agents less suitable for certain areas of application, such as, for example, dispersions of synthetic resins, lacquers, or paints for the preparation of high-gloss or clear films and coatings. In these cases, polyether siloxanes containing silica or alumina cannot suppress the formation of microfoams adquately, which leads to a definite loss of gloss.